The present invention relates to a multilayer fiber light conductor which is especially suitable for use in so-called mode interference methods.
Optical science knows that interferometric devices may be grouped with the most sensitive and most precise measuring devices. This also applies substantially to fiber optical interferometers. In such a fiber optical interferometer a laser functions as a light source, the light of which is polarized and split by a beam splitter to provide two light beams which are passed through two light conductor fibers. One of these fibers functions as the measuring fiber and is thus exposed to the influence of a value to be measured, such as pressure or temperature which causes a change in length or a change in the refractive index of the light conductor fiber, whereby the light travelling through the measuring path is subjected to a phase shift relative to the light passing through a reference path formed by the other fiber which thus serves as a comparing fiber. The light flows or beams exiting at the fiber ends are superimposed at a further beam splitter to be received by two detectors. The detected signals are proportional to cos.sup.2 .DELTA..PHI. and sin.sup.2 .DELTA..PHI.. Electronic circuits including computer circuits well known in the art calculate from these values the phase shift .DELTA..PHI. and thus the value to be measured which is proportional to said phase shift .DELTA..PHI..
A disadvantage of such interferometers which operate with polarized laser light is seen in that two light conductors are required and that two beam splitters must be used, the adjustment of which is rather involved. Additionally, it has been unavoidable heretofore that the polarization states or conditions of the two light conductor flows exiting at the fiber ends differ from each other.